The present invention relates generally to induction heating apparatus, and more particularly to a power switching and control mechanism for use with the induction heating apparatus.
A prior art induction heating apparatus, disclosed in U.S. Pat. No. 3,821,509 which is assigned to the instant assignee comprises an induction heating coil, a power conversion circuit which generates a high voltage ultrasonic frequency wave that drives the induction heating coil, and a full-wave rectifier coupled to an alternating-current power supply to supply the power conversion circuit with a high voltage unfiltered unidirectional potential. The power conversion circuit includes an inverter having a silicon-controlled rectifier and a diode connected in inverse parallel relationship thereto. The silicon-controlled rectifier is triggered by low voltage pulses generated by a trigger circuit coupled to the full-wave rectifier. The induction heating coil generates an alternating magnetic field that produces heat in a utensil located adjacent thereto by inductive coupling.
However, the ON-OFF switching of the induction heating apparatus causes would initiate a large current to flow in the power supply circuit due to generation of the high-voltage ultrasonic frequency wave and sparking occurs between contacts of the switch. If the apparatus employs two or more of the induction heating coils which must be switched on and off independently, sparking may also occur between contacts of the associated switches. This results in wear of contacts and frequent replacement will be required.